A superabsorbent polymer (SAP) is a synthetic polymer material having a function of absorbing water at about 5 hundred times to about 1 thousand times its own weight, and it has been called a superabsorbent material (SAM), an absorbent gel material (AGM), and so on by developing enterprises. The SAP disclosed above initially commercialized for sanitary items and is now being widely used to a water combination soil for horticulture, a water-stop material for civil engineering and construction, a nursery sheet, a freshness preservative in a food distribution field, a poultice material, and the like in addition to the sanitary items like a paper diaper for a child.
The superabsorbent polymer can be prepared through polymerization, drying, pulverization, classification, and surface cross-linking processes. Further, a superabsorbent polymer of which a degree of decrease in absorption capacity is low is advantageous. The degree of decrease in absorption capacity is a value for comparing the absorption speed and the rewetting ability, the absorbed amount during 10 min represents the absorption speed, and the absorbent amount during 3 h means the rewetting prevention ability. When the degree of decrease in absorption capacity is low, absorbed contaminants such as urine do not leak out, and a rash can be prevented.
For this, U.S. Pat. No. 5,624,967 discloses a method of using polyethylene glycol diacrylate (PEGDA) and epoxy resin together as inner cross-linking agents, for preparing an absorbent resin of which the degree of decrease in absorption capacity is low, and it sets the degree of decrease in absorption capacity from 1 to 16. However, examples of the method realize the superabsorbent polymer showing a degree of decrease in absorption capacity of at least about 9, and thus there is a substantial limit in lowering the same. Furthermore, said two or more cross-linking agents including epoxy resin used in the method have difficulty in showing uniform cross-linking distribution in the resin because they have different cross-linking conditions. Moreover, epoxy resin has not recently been used in the preparation of superabsorbent polymers because it is a toxic material.